Filament tensioning device



y 1954 R. J. BLACK ETIAL FILAMENT TENSIONING DEVICE Original Filed July9, 1951 INVENTOR. P4112 (04949121 /P0019 7 1/. 8146A Patented July 27,1954 2,685,045 FILAMENT TENSIONING DEVICE Robert J. Black, Marion, Iowa,and Paul I. Corbell, Palo Alto, Calif., assignors to Collins RadioCompany, Cedar Rapids, Iowa, a corporation of Iowa Original applicationJuly 9, 1951, Serial No.

235,816, now Patent No. 2,656,480, dated October 20, 1953. Divided andthis application December 11, 1952, Serial No. 325,256

2 Claims.

This invention relates in general to filament tensioning devices and inparticular to means for maintaining a filament in a predeterminedposition and shape. This is a divisional case of application SerialNumber 235,816, filed July 9, 1951 which matured as U. S. Patent No.2,656,480 on ously to maintain a filament under tension by. attaching acoil or leaf spring to it, but in very .high power tubes sucharrangements are not satisfactory for the reason that a filament becomesso hot that the spring becomes overheated and loses its flexibility.

It is an object of this invention therefore, to provide a filament whichhas one end integrally formed into a spring to maintain a filament undertension.

Another object of this invention is to provide a filament tensioningdevice wherein the filament is spring loaded by applying a spring biasto a relatively cool portion of the filament.

Yet another object of the invention is to provide a filament tensioningdevice which allows thermal expansion of the filament but maintains thefilament in a predetermined special rela tionship.

A feature of this invention is found in the provision of a filamentmounted between two fixed members with one end of the filament formedinto a coil spring and with a flexible contact enageable with thefilament adjacent the coil spring. A heating potential is appliedbetween one supporting means and the flexible contact.

Another feature of this invention is found in the provision of afilament connected between a fixed point and the periphery of arotatable cam which has a lever arm spring biased so as to tension thefilament. A heating potential is applied between the fixed end of thefilament and an intermediate point adjacent the cam.

Further objects, features and advantages of this invention will becomeapparent from the following description and claims when read in View ofthe drawings, in which;

Figure 1 is a side View of the filament tensioning device of thisinvention;

Figure 2 is a modification of the filament tensioning device of thisinvention; and,

Figure 3 is a detailed top view of the coilspring of Figure 2.

With reference to Figure 1, a filament I0 which might be a ribbon oftungsten for example, has its upper end ll clamped to a supporting meansI2 by the screw l3 and plate [4. The lower end l6 of the filament I0 isconnected by a set screw I! to the periphery of a cam l8.

The cam I8 is rotatably supported by a shaft I9 on a stand-01f 2|, and.the stand-off 2! is in turn connected to a supporting member 22. The camI8 is formed with a lever arm 23 which has an opening 24 formedtherethrough.

A shaft 26 is connected to member 22 and extends through the opening24.. A washer 27 is mounted over the shaft 26 adjacent the lever arm 23.A coil spring 28 is mounted over the shaft 26 and between the Washer 21and a second washer 29. A suitable'holding means, as for example, a nut3| is threadedly received on the shaft 26 and the assembly forms aspring bias against the lever arm 23. It is to be noted that the opening24 is substantially larger than the shaft 26 and thus the lever l8 maypivot about the shaft IS.

A feed-in conductor 32 is connected tothe stand-off 2| and iselectrically connected to the filament ID by clamping means 33. Theclamp 33 comprises clamping plates 34 and 36 and nut and bolt means 31.The lead 32 is flexible so that it will conform to the expansion of thefilament It.

The heating potential is applied between the supporting member I2 andthe supporting member 22, and substantially all of the heating currentflows through the lead 32 to the supporting means 22. The lead 32 has arelatively low resistance and thus the path from the filament ID to thesupporting member 22 will have less resistance than the path through theremainder of the filament l6 and the cam [8.

This allows the lower end I 6- of the filament to remain relatively cooland, thus the tensioning apparatus comprising the cam- I8 and spring 28are not subjected to excessive temperatures. The spring holds thefilament under tension and thus no sagging or bowing is allowed.

Figure 2 illustrates a modification of the invention. The filament IDhas its upper end ll clamped to supporting member l2 and the lower endI6 is integrally formed into a coil spring 46.

The spring 40 is rigidly fastened to a shaft 4| which is mounted to astand-off 42. The shaft 4! is non-rotatably mounted in the stand-off 42and the tension of the spring 40 is maintained so as to hold thefilament ID in tension. The stand-ofi 42 is attached to an extension 43of the member 22 and as best seen in Figure 3, a slot 45 is formed inthe extension 43 to receive the spring therein.

Adjacent the lower end 16, a clamping means 46 is attached to thefilament 10. The clamping means comprises the clamping plates 41 and 48which are held to the filament by a set screw 50. The clamping plate 48is connected to a pair of flexible members 49 and 5|, respectively,which have their opposite ends connected to a projection 52 of themember 22.

A heating potential is connected between the members l2 and 22 and thecurrent flows through the filament l and through the members 49 and tothe member 22. The members 49 and 51 are made of low resistance materialand, thus substantially all of the current flows tothe member 22 throughthem. The spring 40 receives very little current due to the higherresistance of the filament.

As expansion of the filament I0 occurs, due to an increasingtemperature, the spring 40 takes up the slack and the flexible members49 and 5| deflect to maintain the filament under tension. The filamentII] will be maintained substantially fixed relative to the members l2and 22 and there will be no bowing.

It is seen that this invention relates to filament tensioning means andalthough it has been described with respect to particular embodimentsthereof, it is not to be so limited as changes and modifications may bemade therein which are within the full intended scope of the inventionas defined by the appended claims.

We claim: 1. Means for maintaining a filament under tension and in apredetermined spatial relationship between a pair of supporting memberscomprising, one end of said filament integrally formed into a coilspring, said coil spring nonrotatable attached to one of the supportingmembers, the other end of said filament attached to the other supportingmember, a projection attached to the one supporting member adjacent thecoil spring, clamping means attached to the filament adjacent the coilspring, a pair of flexible members connecting said projection with saidclamping means, and said flexible members having a relatively lowelectrical resistance so that they carry substantially all of theheating current.

2. Means for maintaining a filament under tension and in a predeterminedspatial relationship with a pair of supporting members comprising, firstclamping means attaching one end of said filament to one of saidsupporting members, the other end of said filament integrally formedinto a coil spring, said coil spring nonrotatably attached to the othersupporting member, a pair of flexible electrical conducting meansextending from said other supporting member to- Ward said filament,second clamping means attached to said filament adjacent said coilspring and with opposite sides thereof attached to, the free ends ofsaid flexible members toform a pantograph assembly.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,402,797 Wood June 25, 1946 2,546,184 Garner Mar. 27, 1951

